High performance automotive and industrial lubricants are in demand. Accordingly, lubricant manufacturers must provide finished lubricants that exhibit high performance properties. By way of example, premium quality gear oils have very tough low temperature performance specifications as specified by Brookfield viscosities at −40° C. Depending on the application in which the gear oils will be used, they may also need to exhibit a specific viscosity at 100° C. of greater than about 3 cSt.
Finished lubricants, including gear oils, consist of two general components: one or more lubricating base oils and additives. Lubricating base oil is the major constituent in these finished lubricants and contributes significantly to the properties of the finished lubricant. A few lubricating base oils can be used to manufacture a wide variety of finished lubricants by varying the mixtures of individual lubricating base oils and individual additives. By way of example, for gear oils, Brookfield viscosities are typically adjusted by the addition of pour point depressant to the base oil. Specific viscosities at 100° C. are controlled by blending one or more base oils having different viscosities together. To produce high performance finished lubricants, lubricant manufacturers are seeking higher quality lubricant base oil blend stocks.
A growing source of these high quality lubricant base oil blend stocks is synthetic lubricants. Synthetic lubricants include Fischer-Tropsch lubricant base oils, and in the search for high performance lubricants, attention has recently been focused on Fischer-Tropsch derived lubricants. Although Fischer-Tropsch lubricating base oils are desirable for their biodegradability and low amounts of undesirable impurities such as sulfur, the Fischer-Tropsch derived lubricants generally do not exhibit all of the desirable performance characteristics. Although it is well known in the art to improve performance characteristics through the use of additives, these additives are generally expensive and thus, can significantly increase the cost of the lubricant base oil. In addition, the addition of additives may not be sufficient to achieve the desired performance characteristics. By way of example, blends of one or more Fischer-Tropsch base oils with pour point depressants have very high Brookfield viscosities at −40° C. Furthermore, Fischer-Tropsch derived base oils generally are not available in all the desired ranges of viscosity at 100° C. for finished lubricants. Therefore, Fischer-Tropsch derived base oils must be blended with other base oils to optimize the viscosity.
It is well known in the art to produce synthetic lubricants and there have been many developmental attempts at producing synthetic lubricants with high performance characteristics. By way of example, WO 99/41332 and WO 02/070636 are directed to synthetic lubricant compositions used as automatic transmission fluids and methods for producing these synthetic lubricating base stocks. U.S. patent application 10/301,391, filed on Nov. 20, 2002 and assigned to Chevron U.S.A., relates to lubricating base oil blends comprising a low viscosity Fischer-Tropsch derived base oil fraction and a higher viscosity conventional petroleum derived base oil fraction. U.S. patent application 10/743,932, filed on Dec. 23, 2003 and assigned to Chevron U.S.A., discloses a finished lubricant comprising a blend of a Fischer-Tropsch lubricant base oil with high monocycloparaffins and low multicycloparaffins and an additional base oil selected from a group including petroleum derived base oils.
In spite of research into synthetic lubricants, there remains a need for synthetic lubricants comprising Fischer-Tropsch derived lubricant base oils that exhibit high performance, including good low temperature properties.